Vehicles, such as aircraft, include passenger cabins and other compartments enclosed at least partially by lightweight panels. It is necessary for the pilot of such vehicles to communicate with the passengers in the passenger cabin of such vehicles, and therefore such cabins require speaker systems to transmit the pilot's voice, as well as other informational messages, music, motion picture soundtracks and the like.
Traditionally, cone speakers are used as part of a loudspeaker system. Such cone speakers include a driver having a cone driven by a voice coil. Such cone speakers typically are mounted above a ceiling panel over passenger seats in a vehicle. A disadvantage with such cone speakers is that the cone component takes up valuable space above the ceiling panel. Another disadvantage is that it is necessary to cut a hole through the ceiling panel to allow the sound energy generated by the cone to pass through the ceiling panel. In addition, cone speakers project sound at a relatively narrow dispersion angle (±30 degrees). Therefore, for short distance sound projection, such as in an aircraft or other vehicle cabin environment, many cone speakers must be used, and spaced to cover the entire passenger cabin area.
The disadvantages of cone speakers with respect to space, narrow sound projection, and the necessity of cutting a hole through the panel may be overcome by using a flat panel speaker. Currently, there are two types of flat panel speakers: electrostatic speakers and electromagnetic induction (EMI) speakers. However, a disadvantage with electrostatic speakers is that they are dipole, and therefore require openings in both the front and back, and require a thin, soft film diaphragm that is too fragile for use in, for example, an aircraft cabin due to pressure changes during a flight. Electrostatic speakers are coherence speakers and are very directional—making them a poor choice for short distance sound coverage. Further, electrostatic speakers require high voltage—on the order of 2,000 volts—and require heavy metal core transformers. All of this is undesirable for use in applications such as an aircraft cabin. A disadvantage with EMI speakers is that they require a relatively heavy magnetic bar and a printed or wired coil diaphragm. The magnetic bar adds weight to the aircraft. Magnetic field radiation is prohibited for plane use, and the diaphragm, which also must work on dipole principle, is too fragile for use in environments such as an aircraft cabin, and is a coherence speaker, having a projection angle narrower than that of a cone speaker.
Accordingly, there is a need for a loudspeaker system that may take up less space than a conventional cone speaker, not require cutting a hole through a passenger compartment panel, and that is able to project sound over a wider area than current loudspeaker systems.